The present invention relates to electronic ring monitoring devices that activate AC operated signalling devices in response to a ringing signal detected on a telecommunications line. In particular, the present invention relates to an electronic device that monitors the lines from a telephone company or a PBX system and that provides a switched AC output for driving an attached load.
There are a number of different types of telephone systems in use today. Standard copper pair systems utilize a pair of wires, designated "tip" and "ring," connected from the central office (where the routing switches are located) to the subscriber's telephone. In this type of system, a 48 vdc battery voltage is applied between tip and ring, and a 110-130 volt pulsed DC ring signal is applied when necessary to operate the subscriber's ringer. The ring signal typically has a frequency of 20-60 cycles per second. If the subscriber is located within 3 to 4 miles of the central office (known as a "short loop"), there is usually plenty of power in the ring signal to operate a number of telephone ringers or other devices, such as those described in the references cited herein. If the subscriber is located farther away, such as more than 5 or 6 miles from the central office, the power available in the ring signal is substantially reduced, and the addition of loads such as additional telephones or other devices can cause the system to malfunction.
A PBX (private branch exchange) or "key" telephone system is connected to one or more incoming telephone lines (such as copper pair), and it contains switches for connecting a number of extension lines to those incoming lines. The ring signal that is applied to the extension lines by a PBX system ranges from 10-100 volts and 20-30 cycles per second. Because of the typically lower ring voltage used in PBX systems, the power available to run accessories that use the ring signal is substantially lower than on a copper pair system. Consequently, some accessories that are designed to operate on a copper pair system will not function reliably on a PBX system.
A number of types of "carrier" systems are also in use, which are characterized by the use of multiplexing and demultiplexing circuits to place more than one voice channel on a single pair of wires. Both analog and digital multiplexing techniques are used in carrier systems. The ring signals used in carrier systems are at very low power levels compared to those in standard copper pair systems, and the telephones and other equipment used in carrier systems are high impedance, low power devices.
It is desirable to provide a single ringer module that will switch a 120 volt AC load in response to the occurrence of a ring signal on any of the above mentioned types of telephone systems, despite the variations in ring voltage and available ring power on the systems.
There are existing devices that monitor telephone lines and turn on attached visual or audible devices when a ring signal is detected. For example, U.S. Pat. No. 5,157,721 provide a control circuit which detects if the telephone receiver is lifted from the cradle or if the telephone ringer is actuated, and provides a switched power source and response thereto. U.S. Pat. No. 4,747,133 discloses a circuit for operating an electrical light in response to a ring signal or an off-hook condition. U.S. Pat. No. 4,379,210 discloses a ring signal detection circuit that operates an incandescent lamp when ring signal is detected on the telephone line. U.S. Pat. No. 4,467,144 discloses an apparatus for activating a remotely located device under the control of a telephone ring signal, having a relatively sophisticated signal detector and discriminator circuit for deriving ringing signal frequency information and discriminating against dial pulses.
These existing devices have many disadvantages. Such devices are generally reliable in operation only when connected to a standard copper pair telecommunication circuit. Few existing devices, for example, may be connected to PBX systems. Furthermore, existing devices are generally not suitable for driving inductive loads, and they often utilize solid state or mechanical switches without providing adequate isolation between the power switching circuitry and the telecommunications circuitry. Many existing devices are obsolete because of the rapid advances in the technology utilized by the telecommunications industry. Also, known existing devices do not provide the versatility to operate a wide variety of loads from most common types of phone systems.
The telecommunications industry has a need for a device that will overcome these disadvantages. In particular, a device is needed that will work reliably when connected to many different types of telecommunication circuits and that will operate both resistive and inductive loads. The device should be able to discern between a true ringing signal and various types of false signals, and it should be useful in an industrial as well as a residential environment. Further, the device should provide isolation between the telecommunication circuitry and the load driving circuity.